Reducing the effects of residual magnetism in electrical apparatus



Sept. 10,1929. I I w H. L TANNER 1,727,949

REDUCING THE EFFECTS OF RESIDUAL MAGNETISM IN ELECTRICAL APIARATUS Filed Nov. 28} 1924 TIME INVENTOR.

A TTORNEYS.

Patented Sept. 10, 1929.

UNITED STATES PATENT OFFICE.

HARRY L. TANNER, F BROOKLYN, NEW YORK, ASSIGNOR TO FORD INSTRUMENT COMPANY, INC., OF LONG ISLAND CITY, NEW YORK, A CORPORATION OF NEW YORK.

REDUCING THE EFFECTS OF RESIDUAL MAGNETISM IN ELECTRICAL APPARATUS.

Application filed November This invention relates to reducing the effects of residual magnetism in electrical apparatus, particularly of types in which residual magnetism or hysteresis affects the operation of the apparatus aside from power losses.

Apparatus of this character in which the effects of residual magnet-ism are particularly objectional is found in the receivers of signal transmission systems, especially of the types in which rotors or the like are caused to follow the movements of rotatingfields the poles of which follow the movements of the transmitters. In such apparatus as regions of the structure in which the rotating field is produced are successively energized, the residual magnetism in previously energized regions of the structure in conjunction with the newly energized regions will cause the rotors to take up positions due to the resultant effect of the regions which are in any degree effective. In other words, the rotating fields are produced by changes in flux density due to changes in current density, but on account of residual magnetism the flux density at any region is more or less than the value which should be produced by the given current density depending upon whether the density is decreasing or increasing. This causes errors in readings since the indicators associated with the rotors do not occupy the exact positions that they should have in accordance iwilfh the electromotiveforces applied to the windings of the receivers as determined by the transmitting instruments.

It has been proposed to reduce hysteresis losses by superimposing an alternating magnetic field upon a hysteresis cycle that is produced by a slowly varying direct current field. Some experiments have been performed along these lines in which the alternating magnetic field has been produced by passing alternating current through coils separate from In my copending application, Serial No.

those through which the main energizing curs rent passes, so that in effect hysteresis has 28, 1924. Serial No. 752,666.

748,295 filed November 6, 1924, I have de scribed a method of and apparatus for reducing the effects of residual magnetism in electrical apparatus by superimposing. a fluctuating electromotive-force, either alternating or pulsating, upon the electromot-iveforce which is depended upon to cause the apparatus to operate in its intended manner. Inthat application the superimposed electromotive-force, which is shown as an alternating one, may be obtained from a separate source or from the machine which generates the electromotive-force for operating the system to which the invention is applied, but in eachcase the alternating electromotive-force is superimposed upon the main electromotive-force externally of the machine which generates the latter as by means of transformers having their windings in series with the conductors of the system.

The present invention has for its general object the reduction of the effects of residual magnetism in electrical apparatus in which such effects are detrimental from the point of View of accuracy or the like, by the generation in a single machine of a fluctuating electromotive-force equivalent to an alternating electromotive-force superimposed on the electromotive-force which causes the operation of the apparatus, the generated electromotiveforce being impressed on the apparatus to cause its operation and to reduce the effects of residual magnetism in the same way as does the fluctuating electromotive-force which is impressed on the system externally of the machine which generates the electromotive-force for operating the apparatus'as d1sclosed in my copending application re ferred to above.

The particular nature of the invention; as well as other objects and advantages thereof will appear most clearly from a description of a. preferred embodiment which for purpose of illustration will be shown and described in connection with a transmission system'of the character shown in my copending application Serial No. 7 24,912, filed July 8, 1924. g In the accompanying drawing,

Fig. 1 shows a diagrammatic manner the application of the invention to the above mentioned transmission system, and

Figs. 2 and 3 are curves showing the electromotive-force characteristics in the circuits of Fig. 1 under different conditions.

In Fig. 1 '1 indicates generally the transmitter and R the receiver of the system. An armature 1 driven by a suitable sOurce of power and having windings 2 and a commu tator 3 is mounted to rotate between suitable field poles which have been omitted for the sake of simplicity. Engaging the commutator at points 120 apart are three brushes 4, 5 and 6 mounted on but insulated from a ring 7 adapted to be rotated by a pinion 8 to shift the brushes with relation to the field poles of the transmitter.

The windings or coils 2 are connected to the bars of the commutator by conductors 9 which as shown in the figure are disposed symmetrically with respect to a vertical line through the center of the armature, but are differently connected from the top to the bottom of the figure on each side of this center line. At the top of the figure the coils 2 are connected in pairs to adjacent bars of the commutator, then as shown at the right and left hand portions of the figure the coils are connected singly to adjacent bars of the commutator, while finally at the bottom of the figure the coils are connected singly to pairs of bars of the commutator.

From the brushes 4, 5 and 6 conductors 10, 11 and 12 respectively lead to the windings 13, 14 and 15 respectively of the receiver B. These windings constitute a three phase stator and have associated with them a rotor 16 energized from a direct current supply. lVhen the armature 1 is rotating with the brushes 4, 5 and 6 fixed with respect to the field poles of the transmitter certain potential conditions will be set up at the brushes which apply to the conductors 10, 11 and 12 differences of potential corresponding to the instantaneous values in an alternating current circuit. These potential differences at the windings of the receiver set up a magnetic field which acts on the rotor 16 and causes it to assume a certain position with relation to the windings.

It results from the arrangement of the coils 2 and the commutator bars connected to them that under the conditions just stated the electromotive-force between each pair of brushes will be made up of a component of constant value and a fluctuating component of lesser value. This is indicated in Fig. 2 which shows the electromotive-force curve under the conditions assumed, the dotted line A representing the electromotive-force which would be generated were the coils connected to the commutator bars in the usual manner and the full line B representing the electromotive-force actually generated.

Rotation of the brush ring 7 of the trans mitter with resultant shifting of the brushes with respect to the field poles of the receiver will change the potential conditions at the brushes and consequently at the windings of the receiver, thereby producing a rotating magnetic field in the receiver which causes its rotor 16 to follow the movement of the brushes of the transmitter.

Similarly to the previously assumed conditions there will be produced a fluctuating electromotive-force equivalent to an alternating electromotive-force of substantially the same periodicity as under the previous conditions, assuming the speed of the armature to be the same, superimposed in the varying electromotive-force produced by the shifting of the brushes, which causes the operation of the receiver. ,Fig. 3 represents the electromotive-force curve under these new conditions and shows the main electromotive-force component of relatively long period as represented by dotted line C as compared with the period of the superimposed alternating electromotive-force represented by the full line D.

Owing to the residual magnetism in the field structure of the receiver there will be a tendency for the rotor to occupy a position different from that which it should theoretically occupy in accordance with the potential conditions in the receiver windings. This tendency is however substantially overcome by the alternating electromotive-force component which is superimposed upon the more slowly varying electromotive-force component produced by the transmitter, as explained above and indicated in Figs. 2 and 3. Due to the alternating component the residual magnetism in any region of the field structure of the receiver following a period of energization will be substantially reduced, so that the rotor will more nearly assume the position which it should theoretically occupy in accordance with the potential condition in the windings of the receiver, instead of being displaced by the effect of residual magnetism in the field structure.

While the invention has been shown and described in connection with a particular form of transmission system, it will be understood that it may be applied to other systems, and in fact, to other kinds of electrical apparatus in which the effects of residual magnetism should be overcome in so far as they may affect the operation of the apparatus aside from the question of power losses.

I claim 2-- 1. In electrical apparatus, an armature provided with windings, a commutator, brushes arranged for rotation about the commutator and connections between the windings and the se ments of the commutator arranged to generate a fluctuating electromotive-force equivalent to an alternating electromotive-force of constant frequency superimposed on an electromotive-force of lower variable frequency.

' 2. In electrical apparatus, an armature provided with windings, a commutator and 5 means for connecting variable numbers of the windings inversely to variable numbers of the segments of the commutator.

3. In electrical apparatus, an armature provided with windings, a commutator and means for connecting some of said windings in pairs to adjacent segments of the commutator, others of said windings individually to adjacent segments and others of said win ings individually to the segments in pairs.

5 4. In an electrical apparatus, an armature provided with windings, a commutator and means for connecting variable lengths of the windings inversely to variable extents of the commutator.

o 5. In an armature for electrical apparatus, the combination of a bar commutator, coil windings, means severally connecting certain adjacent bars and coils, means severally connecting certain groups of bars to single coils,

and means, severally connecting single bars to certain groups of coils.

6. In electrical apparatus, the combination of an armature provided with commutator segments and windings, brushes arranged for 0' rotation about the commutator segments and connections between the segments and windings to cause the-superimposition upon an operating current of variable frequency of an independent current of constant fre uency.

7. In electrical apparatus, the com ination of an armature having commutator se ments and windings, brushes coacting with the segments, irregular connections between the Segments and windings, and means for moving said brushes relatively to said segmentsto supply constantly fluctuating polyphasecurrent of variable periodicity to an external circuit.

In testimony whereof I aflix my signature.

HARRY L. TANNER. 

